小測試：boost之shared_ptr在容器類std::list中的使用

一個小測試：在std::list容器中使用shared_ptr，演示了對象的添加與刪除的多種方式：通過原始指針(raw pointer)、智能指針（smart pointer）、迭代器(iterator)、boost::enable_shared_from_this等。例子中的代碼只做演示用，實際使用時只用其中的部分做法即可，視應用程序的需要而定。在VS2005及boost_1_37_0下編譯運行通過。

 

#include <list> #include <boost/noncopyable.hpp> #include <boost/enable_shared_from_this.hpp> #include <boost/shared_ptr.hpp> #include <algorithm> #include <iostream> // Task class Task : private boost::noncopyable, public boost::enable_shared_from_this<Task> { public: Task() : id_(0) {} Task(int id) : id_(id) {} virtual ~Task() {} int id() const { return id_; } boost::shared_ptr<Task> ptr() { return shared_from_this(); } public: virtual void run() = 0; protected: int id_; }; // Task1 class Task1 : public Task { public: Task1(int id) : Task(id) {} public: virtual void run() { std::cout << "Task1 id: " << id_ << " running" << std::endl; } }; // Task2 class Task2 : public Task { public: Task2(int id) : Task(id) {} public: virtual void run() { std::cout << "Task2 id: " << id_ << " running" << std::endl; } }; // typedefs typedef boost::shared_ptr<Task> TaskPtr; typedef std::list<TaskPtr> TaskPtrContainer; // ptr_contains_predicate template <typename T> struct ptr_contains_predicate { ptr_contains_predicate(T* pPtr) : mPtr(pPtr) {} template <typename P> bool operator()(const P& pPtr) const { return pPtr.get() == mPtr; } T* mPtr; }; // ptr_contains template <typename T> ptr_contains_predicate<T> ptr_contains(T* pPtr) { return ptr_contains_predicate<T>(pPtr); } // shared_equals_raw template <typename T> struct shared_equals_raw { shared_equals_raw(T* raw) :_raw(raw) {} bool operator()(const boost::shared_ptr<T>& ptr) const { return (ptr.get()==_raw); } private: T* const _raw; }; // run task void run_task(TaskPtr task) { // std::cout << "task id: " << task->id() << std::endl; task->run(); } // print summary void print_summary(TaskPtrContainer& tasks) { std::cout << "task count " << tasks.size() << std::endl; } // application entry int _tmain(int argc, _TCHAR* argv[]) { TaskPtrContainer tasks; // test data for (int i=0; i<10; i++) { if (i % 2 == 0) tasks.push_back(TaskPtr(new Task1(i))); else tasks.push_back(TaskPtr(new Task2(i))); } // run the tasks. std::for_each(tasks.begin(), tasks.end(), run_task); print_summary(tasks); // 10 // // remove by raw pointer // Task* task = tasks.front().get(); tasks.remove_if(ptr_contains(task)); print_summary(tasks); // 9 TaskPtr taskPtr = tasks.front(); tasks.remove(taskPtr); print_summary(tasks); // 8 // remove by iterator task = tasks.front().get(); // TaskPtrContainer::iterator it = std::find_if(tasks.begin(), tasks.end(), ptr_contains(task)); // or TaskPtrContainer::iterator it = std::find_if(tasks.begin(), tasks.end(), shared_equals_raw<Task>(task)); if (it != tasks.end()) { tasks.erase(it); } print_summary(tasks); // 7 // // smart pointer test // TaskPtr ptr(new Task1(100)); tasks.push_back(ptr); print_summary(tasks); // 8 // remove by smart pointer tasks.remove(ptr); print_summary(tasks); // 7 // raw pointer test Task* task1 = new Task1(200); tasks.push_back(TaskPtr(task1)); print_summary(tasks); // 8 // donot use in this way. this will cause double delete. // tasks.remove(TaskPtr(task1)); // #1 wrong!!! tasks.remove_if(ptr_contains(task1)); // ok print_summary(tasks); // 7 // // use enable_shared_from_this // Task* task2 = new Task2(300); // donot use in this way. not a shared pointer until now. // tasks.push_back(task2->ptr()); // #2 wrong!!! tasks.push_back(TaskPtr(task2)); // ok print_summary(tasks); // 8 tasks.remove(task2->ptr()); // #3 correct, problem #1 overcomed print_summary(tasks); // 7 getchar(); return 0; }

 

簡要說明：

• #1、有重複刪除問題，解決的方法是#3，需配合boost::enable_shared_from_this.
• #2、尚未使用shared_ptr，還不能從內部的weak_ptr獲取shared_ptr。
• #3、解決了問題#1